Climbing Stairs

You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

完全是靠列举结果，推出迭代公式，发现就是斐波那契数列的形式，即当n>=3时，f(n)=f(n-1)+f(n-2)。

C++代码实现：

#include<iostream>
using namespace std;

class Solution {
public:
    int climbStairs(int n) {
        if(n==0)
            return 0;
        if(n==1)
            return 1;
        if(n==2)
            return 2;
        int n1=1;
        int n2=2;
        int sum=0;
        while(n>2)
        {
            sum=n1+n2;
            n1=n2;
            n2=sum;
            n--;
        }
        return sum;
    }
};

int main()
{
    int n=5;
    Solution s;
    cout<<s.climbStairs(n)<<endl;
}

运行结果：